|Publication number||US7466115 B2|
|Application number||US 11/231,215|
|Publication date||Dec 16, 2008|
|Filing date||Sep 19, 2005|
|Priority date||Sep 19, 2005|
|Also published as||CN101568893A, EP1938454A2, EP1938454A4, EP1938454B1, US20070063736, WO2007035724A2, WO2007035724A3|
|Publication number||11231215, 231215, US 7466115 B2, US 7466115B2, US-B2-7466115, US7466115 B2, US7466115B2|
|Original Assignee||Texas Instruments Incorporated|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Referenced by (5), Classifications (16), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to power supply circuits. More particularly, the present invention relates to a soft-start circuit and method for power up of an amplifier circuit.
The increasing demand for higher performance power supply circuits has resulted in the continued development of voltage regulator and other power management devices. For example, many low voltage applications require the use of low dropout (LDO) regulators, such as for use in cellular phones, pagers, laptops, camera recorders and other wireless and mobile battery operated devices. These portable electronics applications typically require power management devices having a low voltage and quiescent current flow to facilitate increased battery efficiency and longevity. Such low dropout regulators generally provide a well-specified and stable dc voltage whose input to output voltage difference is low.
With reference to
In the first manner, enable pin ENABLE is connected to input voltage VIN to power-up circuit 100 and turn on output voltage VOUT. With reference to
For dual channel devices, the power-up process becomes more difficult to control. For example, with reference to
In accordance with various aspects of the present invention, a method and circuit for providing a soft start-up process for an amplifier circuit to reduce or prevent destructive overshoot of an output voltage are provided. In accordance with an exemplary embodiment of the present invention, an exemplary method and circuit are configured to suitably momentarily replace an actual fixed reference voltage with a second reference voltage during the start-up process. Such a method and circuit can provide a fast start-up process without destructive overshoot and without affecting or compromising any control loop of the amplifier circuit. Accordingly, an exemplary method and circuit can be configured within various applications and/or retrofitted within existing applications.
In accordance with an exemplary embodiment, an exemplary amplifier circuit is configured with a soft-start circuit, with the soft-start circuit configured to provide a secondary reference voltage during initial start-up before switching to an actual reference voltage. For example, an exemplary start-up circuit can be configured to generate a secondary reference voltage, and then though monitoring of a feedback voltage from an amplifier circuit, suitably switch in the secondary reference voltage and actual reference voltage to provide a controlled start-up process. The secondary reference voltage suitably comprises the minimum amount of voltage required for power-up of the amplifier circuit components to permit operation. In accordance with an exemplary embodiment, the secondary reference voltage can be generated by current source configured with a temperature compensating circuit to provide fast and reliable power source; however, the secondary reference voltage can also be generated in various other manners and configurations.
In accordance with an exemplary embodiment of the present invention, the soft-start circuit suitably comprises a second reference voltage, a switching circuit, and a logic circuit. In such an embodiment, the start-up circuit is configured to generate a secondary reference voltage, and then though monitoring with the logic circuit the feedback voltage from the amplifier circuit, use the switching circuit to suitably switch in the secondary reference voltage. Once the feedback voltage meets or exceeds the secondary reference voltage, soft-start circuit can suitably switch in the actual reference voltage. As a result, destructive overshoot of the output voltage can be suitably reduced or eliminated.
A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in connection with the Figures, where like reference numbers refer to similar elements throughout the Figures, and:
The present invention may be described herein in terms of various functional components and various processing steps. It should be appreciated that such functional components may be realized by any number of hardware or structural components configured to perform the specified functions. For example, the present invention may employ various integrated components, such as buffers, current mirrors, and logic devices comprised of various electrical devices, e.g., resistors, transistors, capacitors, diodes and the like, whose values may be suitably configured for various intended purposes. In addition, the present invention may be practiced in any integrated circuit application. However for purposes of illustration only, exemplary embodiments of the present invention will be described herein in connection with a low dropout regulator for use with power supply circuits. Further, it should be noted that while various components may be suitably coupled or connected to other components within exemplary circuits, such connections and couplings can be realized by direct connection between components, or by connection through other components and devices located thereinbetween.
In accordance with various aspects of the present invention, a method and circuit for providing a soft start-up process for an amplifier circuit can suitably reduce or prevent destructive overshoot of an output voltage that can occur when a power management device is turned on. In accordance with an exemplary embodiment, an exemplary method and circuit can be configured to momentarily replace an actual fixed reference voltage with a secondary reference voltage during the start-up process of the amplifier circuit. Such a method and circuit can be utilized without affecting or compromising the control loop of the amplifier circuit.
Such a method and circuit can be useful in various applications. For example, an exemplary method and circuit for providing a soft-start process can suitably reduce destructive overshoot in dual channel amplifier circuits, such as dual channel LDO regulator circuits, having a single bandgap reference voltage. An exemplary method and circuit for providing a soft-start process can also be configured within any other amplifier circuit application where a controlled start-up process is desirable.
In accordance with an exemplary embodiment, with reference to
Soft-start circuit 504 is configured to provide a secondary reference voltage during initial start-up of amplifier circuit 500 before switching to an actual reference voltage. For example, soft-start circuit 504 can be configured to generate a secondary reference voltage V2, and then through monitoring of feedback voltage VFB from error amplifier circuit 506, suitably switch in secondary reference voltage V2 and an actual reference voltage to provide a controlled start-up process. The actual reference voltage can comprise various types of reference voltages, such as an actual silicon bandgap voltage VBG of approximately 1.2 volts, divided down silicon bandgap voltages of 0.4V and higher, partial VBE bandgap voltages of approximately 0.6V, and other variable references voltage up to 5 volts or more. Soft-start circuit 504 can utilize various switching configurations, represented by switches S1 and S2, for switching in secondary reference voltage V2 and bandgap voltage VBG.
Initially, soft-start circuit 504 begins with secondary reference voltage V2 being switched in as a reference voltage to the positive input terminal of error amplifier 506 until such time that feedback voltage VFB exceeds secondary reference voltage V2, and then can suitably switch in bandgap voltage VBG for the remainder of ramping up of output voltage VOUT. As a result, the output voltage will ramp upwards following secondary reference voltage V2 before transitioning and then will continue to ramp upwards to the level of feedback voltage VFB, thus reducing or eliminating destructive overshoot. Moreover, such control of the start-up process can be realized without any effect or compromise to the control loop of error amplifier 506.
Secondary reference voltage V2 suitably comprises the minimum amount of voltage required for power-up of the amplifier circuit components to permit operation. In effect, secondary reference voltage V2 acts as a “virtual” bandgap reference voltage that suitably replaces bandgap voltage VBG. Secondary reference voltage V2 is suitably configured to be generated faster than bandgap voltage VBG, since secondary reference voltage V2 must be quickly used not only when bandgap voltage VBG is already on, but also when both are turned on simultaneously, i.e., secondary reference voltage V2 should be generated quickly since it is utilized before bandgap voltage VBG. In addition, secondary reference voltage V2 is configured at a voltage level below that of bandgap voltage VBG, for example well below the final bus voltage used to drive error amplifier 506. Configuring secondary reference voltage V2 with lower current power dissipation can also be beneficial. In addition, secondary reference voltage V2 can also be provided with higher noise limitations, and allow for lower noise requirements to achieved later once noise reduction capacitors within amplifier circuit 500 are fully charged.
In accordance with an exemplary embodiment, with reference to
An exemplary soft-start circuit 504 can be configured in various manner for switching a secondary reference voltage and actual reference voltage to an amplifier circuit. For example, with reference to
Secondary reference voltage circuit 710 can suitably comprise any circuit configured for generating a voltage reference that is lower than a primary voltage reference, e.g., an actual bandgap voltage 712. In accordance with an exemplary embodiment, secondary reference voltage circuit 710 is also configured to be generated faster than actual bandgap voltage 712 and/or with lower current power dissipation. For example, secondary reference voltage circuit 710 can comprise voltage reference circuit 600 or any other circuit for generating a secondary reference voltage comprising the minimum amount of voltage required for power-up of amplifier circuit 700 to permit operation.
Logic circuit 714 is suitably configured for monitoring feedback voltage VFB and for determining the appropriate time for switching in secondary reference voltage circuit 710 and actual bandgap voltage 712. In accordance with an exemplary embodiment, logic circuit 714 comprises a comparator configured for measuring feedback voltage VFB and comparing its value to the value of the secondary reference voltage generated by secondary reference voltage circuit 710, and a timing circuit configured for control of switch circuit 716. Logic circuit 714 can suitably control switch circuit 716 to switch in secondary reference voltage circuit 710 and actual bandgap voltage 712. Logic circuit 714 and any comparators or timing circuits can comprise various configurations for providing the intended functions.
Switch circuit 716 is suitably configured for switching in secondary reference voltage circuit 710 and actual bandgap voltage 712, and can comprise any type of devices or components for providing switching functions. Switch circuit 716 can also be configured with filtering and other like functions to address any noise or other detriments caused by switching functions.
With additional reference to
Once feedback voltage VFB increases to meet or exceed the secondary reference voltage (as represented by 806), logic circuit 714 can suitably control switching circuit 716 to switch in the actual reference voltage VBG for reference voltage VREF, in effect latching to reference voltage VBG to prevent any impact from further oscillation of feedback voltage VFB. Reference voltage VREF will then suitably ramp upwards until reaching the level of bandgap voltage VBG (as represented by 808) and remain at that level until amplifier circuit 700 is powered down or disabled.
In the case of large noise reduction capacitors, the charging of which can be prolonged depending on the internal circuit design, the reference voltage can be held at the voltage V2, e.g., the virtual bandgap voltage, until actual reference voltage VBG ramps upwards to within a final tolerance.
As a result, a fast start-up of amplifier circuit 700 can be realized, e.g., within approximately 50 microseconds, while destructive overshoot of output voltage VOUT can be suitably reduced or eliminated, as well as any delay from charging the noise reduction capacitor. In addition, such elimination of the destructive overshoot can be realized without affecting or compromising the dynamics of the control loop for LDO circuit 702. Such arrangements can be beneficial in a wide variety of applications, and in particular, within dual channel LDO circuit applications with independent enable pins and a single bandgap reference voltage.
The present invention has been described above with reference to various exemplary embodiments. However, those skilled in the art will recognize that changes and modifications may be made to the exemplary embodiments without departing from the scope of the present invention. For example, the various exemplary embodiments can be implemented with other types of power supply circuits in addition to the circuits illustrated above. These alternatives can be suitably selected depending upon the particular application or in consideration of any number of factors associated with the operation of the system. Moreover, these and other changes or modifications are intended to be included within the scope of the present invention, as expressed in the following claims.
|Cited Patent||Filing date||Publication date||Applicant||Title|
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8710813 *||Apr 8, 2009||Apr 29, 2014||System General Corp.||Low drop-out regulator providing constant current and maximum voltage limit|
|US8729877 *||Sep 13, 2011||May 20, 2014||Texas Instruments Incorporated||Fast startup algorithm for low noise power management|
|US9350240||Apr 8, 2014||May 24, 2016||Texas Instruments Incorporated||Power converter soft start circuit|
|US20090256540 *||Apr 8, 2009||Oct 15, 2009||Ta-Yung Yang||Low drop-out regulator providing constant current and maximum voltage limit|
|US20130063110 *||Sep 13, 2011||Mar 14, 2013||Texas Instruments Incorporated||Fast startup algorithm for low noise power management|
|U.S. Classification||323/280, 323/273|
|International Classification||G05F1/40, G05F1/56|
|Cooperative Classification||H03F1/523, H03F1/305, H03F3/45183, H03F1/52, H03F2200/393, H03F2200/78, H03F1/02|
|European Classification||H03F1/52, H03F3/45S1B1, H03F1/30E, H03F1/02, H03F1/52B|
|Sep 19, 2005||AS||Assignment|
Owner name: TEXAS INSTRUMENTS INCORPORATED, TEXAS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:BIAGI, HUBERT J.;REEL/FRAME:017022/0687
Effective date: 20050919
|May 25, 2012||FPAY||Fee payment|
Year of fee payment: 4